Fifteen-year-old Robbie Sumner meets Heather at a summer camp in Featherstone Castle and the two become friends. But then a series of strange events takes place at the castle. Heather is visited by a ghostly figure who warns her, «Be careful! There is danger in the water!» An exciting adventure unfolds as Robbie and Heather set out to uncover the ghost’s identity and the meaning behind its terrifying words.